The proposed experiments are directed towards a molecular understanding of the specialized recombination events attributeable to the prokaryotic kanamycin resistance transposon Tn5 in E. coli and, more generally, to the understanidng of the evolution of antibiotic resistance transposons and their component genes. We will employ genetic and molecular approaches to: (19 generate a transposase gene (tnp)-1ac operon fusion in Tn5 and use it to learn how tnp transcription is regulated, obtain tnp nonsense mutants, and produce large quantities of transposase protein in vivo: (2) determine conditions under which the Tn5 encoded transpospase limits the rate of transposition in vivo: (3) detect transposase activity in vitro; (4) test current models of transposon stimulated deletion formation; (5) examine the structural, physiological and genetic factors which control the rate of Tn5 excision; (6) learn whether components of Tn5 retain the capacity for transposition by themselves, in the absence of intact Tn5: and (7) detect and characterize new aminoglycoside resistance transposons in Gram negative clinical isolates.